1. Field of the Invention
The invention relates to a method for acquiring traffic situation data in a network of traffic routes which is covered by a cellular mobile radio network comprising a multiplicity of base stations and in which a multiplicity of vehicles is moving which are in each case provided with an operating mobile terminal for the mobile radio network, particularly a mobile telephone, in which method information about signal transit times between the terminals at the base stations is acquired and used for estimating the current location of individual terminals.
2. Description of the Prior Art
Numerous methods for acquiring traffic situation data are known in which these data are picked up by vehicles, which participate in the road traffic as a fleet of sample vehicles, and are reported to a central station by means of mobile radio, specifying the current vehicle position. The data transmitted to the central station usually contain information on the position of the vehicle and its speed. The current vehicle position is determined in the vehicle itself by using, for example, a satellite navigation system (e.g. GPS). Since a reliable detection of the traffic situation requires a large number of vehicles of the fleet of sample vehicles, the data traffic between the vehicles and the central station results in considerable expenditure. To limit this expenditure, it is known, for example from EP 0 715 285 B1, to provide the vehicles of the fleet of sample vehicles, from the central station, with advance information about the conditions under which a data transmission from the vehicles to the central station is to be undertaken so that the data traffic can be largely restricted to the cases of disturbances of the traffic flow.
Nevertheless, this method entails not only considerable loading on the channels of the mobile radio network used but, moreover, also requires special equipment in the individual vehicles of the fleet of sample vehicles.
From DE 198 36 778 A1 , a method is known for locating mobile telephones in a mobile radio network by triangulation on the basis of signal transit times between the mobile telephone and a number of base stations within the transmitting area of which the mobile telephone is located. In so-called TDMA mobile radio systems, the transit time of each radio link between the mobile terminal and the base stations of the mobile radio network is determined for the purpose of aligning the terminal synchronization, that is to say the phase of the TDMA frame at the terminal. Since the transit time of the signal is representative of the distance between the terminal and the respective base station, the location can be determined very simply, in principle, if the distances to a number of base stations are known. There is thus a possibility of determining the current geographical position of the respective terminal relative to the known geographic positions of the base stations. In principle, the locating can therefore also be done without using a GPS system but, in general, the accuracy is lower because of the limited resolution (approx. 500 m). In centers of population, in particular, it would not be possible to unambiguously correlate a mobile terminal, which is in a vehicle on a road, with this road because of this limited accuracy.
In DE 198 36 089 A1, a method for determining dynamic traffic information is described in which the base stations of a mobile radio network which are set up in a network of traffic routes estimate the respective distance to a mobile terminal by means of the received signal strength and infer movements of the mobile terminal via the change in signal strength. The resolution of this method is comparatively coarse and therefore less suitable, particularly for traffic networks with a high density of traffic routes. However, it is also advantageous in this method that no special terminals need to be available in the individual vehicles but the presence of, for example, an operating mobile telephone in the vehicle is sufficient.
A further method for acquiring traffic situation data by means of mobile radio networks is known from DE 196 38 798 A1. In this document, a method is described in which operating parameters in the mobile radio network, e.g. the number of handovers at the boundary between two cells on a road, are selectively evaluated. The evaluated operating parameters relate to operating sequences and states in the mobile radio network and are correlated with certain traffic conditions in the network of traffic routes. In an initialization phase, data are collected over a relatively long time and processed to form “profiles”. In the phase of utilization, the operating parameters of the mobile radio network which are currently detected are compared with these profiles and any deviations found which do not indicate normal traffic conditions are reported to a traffic control center. The disadvantageous factor in this method is that the resolution during the evaluation of handovers at cell boundaries cannot be reliably reproduced. In addition, the cell boundaries are naturally arranged to be stationary and thus do not provide an approach to a method which would be comparable with an acquisition of traffic situation data by means of a fleet of sample vehicles. The cell boundaries cannot everywhere be unambiguously mapped onto certain road segments so that this known method appears to be meaningfully useable only within local limits and outside of population centers.